The present invention relates to an electromagnetic coupling apparatus for intermittently performing transmission of rotational torque and braking of a rotating member by intermittently exciting an excitation coil.
(1) In an electromagnetic coupling apparatus such as an electromagnetic clutch or an electromagnetic brake, a conventional excitation unit for magnetically attracting an armature is designed as disclosed in, e.g, Japanese Utility Model Publication No. 60-39540.
This excitation unit is housed in an annular groove of a yoke through an insulating resin material, and is constituted by a resin coil bobbin and an excitation coil wound therearound. The coil bobbin is constituted by a cylindrical portion and flanges on both the sides thereof so as to have an annular shape having a U-shaped section as a whole. The wires of the excitation coil are wound around the coil bobbin by a plurality of turns by using a winding machine. Portions of the turn start and end portions of the excitation coil and leads which are soldered to the start and end portions are covered with insulating tubes. The yoke for housing the coil bobbin around which the excitation coil is wound is pressed into an annular shape. The yoke is constituted by a bottom plate and outer and inner flanges so as to form an annular groove and to have a substantially U-shaped section. The outer and inner flanges are tapered such that inner circumferential surfaces expand toward the opening side. Recesses are formed in the inner circumferential surfaces. A projection is formed on the annular bottom plate and extends into the annular hole, and a rubber bush is fitted in a hole formed in the bottom plate.
With this arrangement, the coil bobbin having the excitation coil wound therearound is loosely fitted in the annular groove of the yoke. After the leads of the excitation coil are inserted into the hole of the rubber bush and are extracted outside, an insulating resin material is injected into a portion around the coil bobbin and is hardened. As a result, the excitation coil is insulated and fixed in the annular groove of the yoke. In this case, since the projection is formed on the bottom plate of the annular groove so as to lift the coil bobbin from the bottom plate, the resin flows into the bottom plate side of the coil bobbin. In addition, since the recesses are formed in the inner circumferential surfaces of the flanges defining the annular groove, the resin flows into the recesses, the resin is not separated from the coil bobbin.
(2) In an electromagnetic clutch as an electromagnetic coupling apparatus mounted in a coolant compressor as, e.g., a vehicle cooling apparatus, a pair of terminals are formed in a resin terminal base fixed to the rear surface of a yoke by insert molding. An excitation coil is connected to an external electrical circuit through these terminals.
As an electromagnetic coupling apparatus of this type, for example, an apparatus disclosed in Japanese Utility Model Publication No. 57-26980 is known. An excitation unit arranged in this electromagnetic coupling apparatus has the following arrangement. A hole communicating with a through hole of a coil bobbin is formed in an annular groove bottom surface of a yoke for housing an excitation coil wound around the coil bobbin. The turn start and end portions of the excitation coil are extracted outside from this hole. A box-like resin terminal base is mounted on the coil bobbin by fitting a protruding opening portion of the terminal base in the through hole. The terminal base is fitted in a groove of a mounting plate, and is fixed to the rear surface of the yoke through a partially cut upright portion formed at the groove portion. In addition, a pair of terminals are integrally formed in the terminal base by insert molding. The turn start and end portions of the excitation coil are respectively fixed to the pair of terminals by caulking, and are electrically connected to leads fixed to the pair of terminals by caulking. The coil bobbin and the terminal base having the above-described arrangements are fixed with a caulking piece formed on an opening portion of the annular groove and a caulking piece formed at the groove portion. At the same time, a resin is injected on externally exposed portions of the excitation coil, and the connecting portions between the turn start and end portions of the excitation coil extracted into the terminal base and the terminals, and into the through hole of the yoke, thereby preventing an insulation failure or disconnection of the excitation coil and the connecting portions.
With this arrangement, the coil bobbin around which the excitation coil is wound is loosely fitted in the annular groove of the yoke, and the turn start and end portions of the excitation coil are extracted to the terminal base and connected to the terminals. Thereafter, the resin is injected on the externally exposed portion of the excitation coil and the connecting portions between the turn start and end portions of the excitation coil extracted into the terminal base and the terminals, and into the through hole of the yoke. As a result, the excitation coil is insulated and fixed in the annular groove of the yoke.
(3) In an electromagnetic clutch mounted in a coolant compressor as, e.g., a vehicle cooling apparatus, since the lengths of leads vary depending on a wiring state with respect to other auxiliary units in the vehicle, versatility of a clapper electromagnet is poor in terms of design and is uneconomical. In addition, in an electromagnetic clutch of this type, a surge killer diode is incorporated in an electrical circuit of an electromagnet. Since the diode is incorporated in the electromagnet or arranged outside the electromagnet, versatility of the electromagnet is also poor and is uneconomical.
An electromagnetic coupling apparatus for solving such problems, for example, is disclosed in Japanese Utility Model Publication No. 63-6512. This apparatus comprises an electromagnet constituted by a yoke in which an excitation coil is fixed in annular groove with an epoxy resin material or the like, and a terminal base fixed to the rear surface of the yoke with through a partially cut upright portion of a mounting plate joined to the rear surface of the yoke by solvent welding. Terminals which are formed in the terminal base by insert molding are constituted by connecting portions connected to the excitation coil, and connecting portions connected to an external electrical circuit. When the electromagnet of the electromagnetic coupling apparatus having the above-described arrangement is to be assembled, the terminal base is tentatively fixed to the yoke by bending the partially cut upright portion formed on the outer side of the mounting plate. The turn start and end portions of the excitation coil are hooked on lock pieces formed on the connecting portions as partially cut upright portions of the terminals. Subsequently, the excitation coil and the lock pieces are integrally joined to each other by soldering or fusing. A metal lid is fitted on the terminal base. The terminal base and the lid are fixed to the yoke by expanding partially cut upright portions formed on the inner side of the mounting plate by caulking.
For example, Japanese Patent Laid-Open No. 57-51026 discloses another electromagnetic coupling apparatus. In this apparatus, a lead extracted from an electromagnet is connected to a terminal of a resin-molded surge killer diode. An external electrical circuit is connected to the electromagnet through this terminal. The ground side of the lead is fixed to a housing of a coolant compressor by integrally fixing a distal ground terminal and a resin-molded ground piece to the housing with screws.
In the conventional electromagnetic coupling apparatus described in item (1), in order to prevent an insulation failure caused by moisture which enters the excitation coil, the insulating resin material is injected between the annular groove of the yoke and the coil bobbin, as described above. Since such an operation is time-consuming, productivity is decreased, and it demands a great deal of labor.
In the conventional electromagnet coupling apparatus described in item (2), the resin is supplied to the exposed portions of the excitation coil, the connecting portions between the turn start and end portions of the excitation coil and the terminals, and the through hole of the yoke in order to prevent an insulation failure or disconnection due to vibrations or the like, as described above. Since a molding operation is required in the process of manufacture, and a long period of time must be consumed, productivity is decreased, and it demands a great deal of labor.
In the conventional electromagnetic coupling apparatus described in item (3), as a countermeasure against vibrations of a vehicle engine or vibrations during travel, a pair of terminals are formed in the resin terminal base by insert molding, and only the connecting portions to be connected to an external electrical circuit are caused to protrude into the U-shaped space side. In addition, the excitation coil and the terminals are connected to each other in the following manner. The lock pieces which are integrally formed by bending are arranged on the inner wall formed between the pair of connecting portions connected to the excitation coil and the connection portions of the terminals, and the turn start and end portions of the excitation coil are guided between the inner wall and the side surfaces of the lock pieces into the terminal base. Thereafter, the start and end portions are firmly connected to the terminals while mechanically and electrically satisfactory contact areas are ensured.
In such a structure, however, since the inner wall is present between the connecting portions or the integrally bent portions as partially cut upright portions are formed to extend upward from the terminals, the space in the terminal base cannot be effectively used.
In addition, in such an electromagnetic coupling apparatus, the interior of the terminal base must be waterproofed. However, in the conventional apparatus in which the metal lid is fixed to the resin terminal base by caulking the partially cut upright portions of the mounting plate, good quality is difficult to ensure, and problems are posed in terms of reliability.
Furthermore, when a diode is to be mounted, the diode is resin-molded to a terminal and is integrally formed by insert molding in order to provide a countermeasure against vibrations and to ensure waterproof. If such a molding operation is performed in the process of manufacture, a lead time is prolonged, operation efficiency is degraded, and problems are posed in terms of cost.